The present invention concerns amplifiers with low-noise and low-power characteristics, particularly common-gate amplifiers for wireless communications.
Today there are a wide variety of computer and telecommunications devices, such as personal computers (PCS), mobile telephones, and personal data assistants (PDAs), that need to share information with each other. Typically, this information is shared using electrical cables connecting one device to another.
However, in recent years, it has become increasingly desirable and practical to replace the awkward cable connections with wireless (radio) communications links between devices. Evidencing this expansion in wireless connectivity is the growing acceptance of several standards for wireless voice and data communications, such as the Institute of Electrical and Electronic Engineers (IEEE) 802.11 wireless standards, the HomeRF standards, and the Bluetooth wireless standard. (HomeRF is a trademark of the HomeRF Working Group, Inc. of Portland, Oreg.; Bluetooth(trademark) is a trademark owned by Telefonaktiebolaget L M Ericsson of Sweden.)
Bluetooth wireless technology holds the promise of allowing users to simply turn on their electronic devices and have them automatically and instantaneously establish wireless communications with other nearby Bluetooth-compliant devices. For example, it is expected that one will buy a compliant printer, take it home, turn it on, and have it automatically establish a wireless connection with a nearby computer, mobile telephone, digital camera, and/or personal digital assistant, enabling all these devices to print data on the printer from anywhere in the home.
One vital component to the function of Bluetooth-compliant devices as well as other devices with wireless connectivity is the radio receiver that receives transmitted signals. Although the receiver includes numerous components of relatively great complexity, none are more essential than a low-noise amplifierxe2x80x94the circuit that receives input signals from the antenna, and amplifies or scales the signals to make it easier to detect the information they carry.
Two important traits of these amplifiers is their power consumption and noise performance. Lower power consumption is desired, particularly in battery-powered devices, to extend battery life. And, excellent noise performance is desired to avoid masking or corrupting communication signals with noise from the amplifiers.
In one conventional form of amplifier, known as a common-gate amplifier, extra bias circuitry has typically been added to bias (or shift) transistors in the amplifier to an active operating region, thereby reducing distortion of received signals. However, the extra bias circuitry not only consumes considerable surface area on an integrated circuit, but also increases power consumption and introduces noise into the amplifier.
Accordingly, there is a need for better common-gate amplifiers for radio in radio receivers, particularly Bluetooth-compliant radios.
To address these and other needs, the present inventor devised several unique common-gate amplifiers. In particular, one exemplary common-gate amplifier includes a field-effect transistor, a current source, and an inductor. The field-effect transistor includes a gate, a drain, and a source. The current source is coupled between a supply node and the drain, and the inductor is coupled between the gate and the source. The inductor behaves as a short circuit at low frequencies, forcing the field-effect transistor to function as a diode and thus eliminates the need for additional circuitry to bias the transistor. To this extent, the amplifier is considered self biased.
The exemplary embodiment further includes a load circuit coupled between the source of the field-effect transistor and another supply node. One exemplary load circuit comprises a field-effect transistor with a feedback resistor between its control gate and one of its non-control nodes. The resistor effectively configures the transistor as a diode, allowing it to exhibit a self-biasing characteristic and thus eliminating the need to apply a separate bias voltage to the transistor.
Other aspects of the invention include a receiver, a transceiver, and an electronic device incorporating amplifiers of the present invention. Another aspect is a programmable integrated circuit having a transceiver and one or more programmable logic devices.